This application claims the benefit of and priority from Japanese Application No. 2001-360377 filed Nov. 27, 2001, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention pertains to a brake hose having two reinforcing yarn layers including a lower yarn layer and an upper yarn layer in a rubber base.
2. Description of the Related Art
A brake hose known in the conventional art is shown in FIG. 7 (JP 06-201076A). FIG. 7 is a cross-section of the main components of a conventional brake hose 200. Because the brake hose 200 must have high resistance against brake fluid pressure, it is formed from several layers of rubber and fiber yarn. The brake hose 200 comprises an inner tube rubber layer 202, a lower yarn layer 204, an intermediate rubber layer 206, an outer yarn layer 208, and a cover rubber layer 210.
The brake hose 200 is required to meet a higher pressure resistance standard than a coolant system hose or a fuel system hose. As fluid temperatures and pressure levels of automobile system have increased in recent years, the demand for higher pressure resistance has increased as well.
The pressure from the fluid flowing in the flow path 201 inside the brake hose 200 is transmitted from the inner circumference area of the brake hose 200 to the outer circumference area thereof. In other words, the pressure is transmitted to the inner tube rubber layer 202, the lower yarn layer 204, the intermediate rubber layer 206, the upper yarn layer 208 and the cover rubber layer 210, causing each layer to expand. Each layer has a binding force that operates against the pressure exerted by the fluid and inhibits expansion of such layer. The inner tube rubber layer 202, the intermediate rubber layer 206 and the cover rubber layer 210 are highly elastic, and are responsible for no more than 10% of the total binding force, while the majority of the binding force is possessed by the lower yarn layer 204 and the upper yarn layer 208. Consequently, increasing the binding force of the lower yarn layer 204 and the upper yarn layer 208 increases the durability and expansion resistance (i.e., resistance to cubical expansion) provided by the brake hose 200. As a result, increasing both of these characteristics by changing the type of yarn material used and the braiding method of the yarn layers has been examined.
An object of the present invention is to provide a brake hose that offers increased durability and expansion resistance.
In accordance with one embodiment of the present invention, a brake hose comprises reinforcing layers in a rubber base. The brake hose comprising an inner tube rubber layer that is made of a rubber material and has a flow path for flowing fluid; a lower yarn layer formed by braiding lower yarn around the inner tube rubber layer; an intermediate rubber layer made of a rubber material and located around the lower yarn layer; an upper yarn layer formed by braiding upper yarn around the intermediate rubber layer; and a cover rubber layer formed around the upper yarn layer. The intermediate rubber layer is formed from a sheet material having a Mooney viscosity of 10-40 Mv (minimum Mooney value) at 145xc2x0 C.
The Mooney viscosity is a value reflecting measurement of the viscosity of non-vulcanized rubber at 145xc2x0 C. based on the K6300 test promulgated under JIS (Japanese Industrial Standards).
In the brake hose pertaining to the present invention, the pressure exerted by the fluid flowing in the flow path is transmitted from the inner circumference area of the brake hose to the outer circumference area thereof, i.e., from the interior of the rubber base to the lower yarn layer and the upper yarn layer, causing each such layer to expand. A binding force that restricts the expansion of the brake hose in resistance to the pressure from the fluid is generated. The rubber base is responsible for no more than 10% of the total binding force due to its high elasticity, while the majority of the binding force is exerted by the lower yarn layer and the upper yarn layer.
It is preferred that the intermediate rubber layer 16 have a thickness of 0.1-0.25 mm. This is because if the thickness is less than 0.1 mm, the intermediate rubber layer 16 becomes too thin and cannot be braided around the lower yarn layer 14, while if the thickness exceeds 0.25 mm, the intermediate rubber layer is so thick that the intermediate rubber layer 16 functions as an elastic layer that permits displacement of the lower yarn layer 14, and the displacement-inhibiting effect of the lower yarn layer is diminished.
As the rubber material for the sheet, EPDM, isobutylene-isoprene copolymer rubber (IIR) or natural rubber (NR) may be used. Using EPDM or IIR or a material comprising a mixture of the two permits a higher heat resistance because of the properties of such materials. EPDM refers to ethylene-xcex1-olefin-unconjugated diene copolymer (propylene as xcex1-olefin).
In a preferred embodiment of the intermediate rubber layer, such layer is formed to a thickness of 0.1-0.25 mm through the application of rubber cement. Rubber cement has a Mooney viscosity of 0, and can be sufficiently impregnated between the lower yarn strands of the lower yarn layer, thereby preventing displacement of the lower yarn. By forming the intermediate rubber layer formed from rubber cement to the above thickness, the intermediate rubber layer is sufficiently impregnated among the strands of the upper yarn of the upper yarn layer, and the desired operation and effect can be obtained.